Method for cleaning objects with solvent



Aug. 12, 1969 D. J. BARDAY 3,

METHOD FOR CLEANING OBJECTS WITH SOLVENT Original Filed Oct. 12, 1964INVENTOR D0167, J fiacrciagy ATTORNEYS United States Patent U.S. Cl.13431 6 Claims ABSTRACT OF THE DISCLOSURE A degreasing method in whichthe more volatile component of a solvent liquid mixture is selectivelyflash evaporated from the heat emitting section of a heat pump togenerate vapor to rinse the objects washed in the solvent liquidmixture. A blanket of air vapor mixture is maintained at the top of atank above a saturated vapor zone in turn above the solvent liquid. Theair vapor blanket is maintained by continuously withdrawing some of it,condensing solvent vapor from it in the heat absorbing section of theheat pump and then returning the remaining air vapor mixture to theblanket. The condensed solvent is utilized for rinsing.

CROSS-REFERENCE TO RELATED APPLICATION This application is a division ofcopending application S.N. 403,142, filed Oct. 12, 1964 by this sameinventor, now Patent No. 3,308,839 dated Mar. 14, 1967.

BACKGROUND OF THE INVENTION This invention relates to a method forcleaning objects by contacting them with a fluid solvent and, it moreparticularly relates to a vapor degreasing type of such method.

Pre-existing vapor degreasers drastically heat the liquid solvent in thewash tank to generate a vapor zone above it. This introducescontaminants into the vapor zone and promotes vapor losses, which becomesignificant when more expensive solvents are utilized. This solvent lossis particularly serious with respect to the fiuorinated hydrocarbons andthe more volatile chlorinated hydrocarbons and which have quiteadvantageous cleaning properties. They leave little or no residue oncleaned parts upon evaporation and are not injurious to plastics, codemarkings, electrical insulating materials, and the like, but they arerelatively expensive. This makes it uneconomical to tolerate the normallosses occurring in industrial cleaning from vapor losses and solventcontamination. Such fiuorinated hydrocarbon solvents aretrichloromonofluoromethane, trichlorotrifiuoroethane,tetrachlorodifiuoroethane, or any mixture of them. Such chlorinatedhydrocarbon solvents are methyl chloroform, methylene chloride, carbontetrachloride, or any mixture of them and the fluorinated hydrocarbonsolvents. Other advantageous mixtures may contain alcohol or arelatively non-volatile chlorinated hydrocarbon such astrichloroethylene.

An object of this invention is to provide an eflicient, simple andeconomical method for cleaning objects by contacting them with a fluidsolvent.

Another object is to provide such a method of the vapor degreasing type.

A further object is to provide such a method that minimizes solventlosses and makes it possible to economically utilize the efficient, morevolatile and expensive cleaning solvents.

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SUMMARY In accordance with this invention, the vapor zone in a vapordegreaser is maintained by flash evaporating the solvent liquid from afine spray at temperatures below the normal boiling temperature of abody of the liquid. This minimizes the carryover of contaminants fromliquid into the vapor, facilitates dense saturation of the vapor zoneand makes it possible to selectively evaporate the more volatile from amixture of solvents. A more volatile and expensive solvent can thus bemixed with a less volatile and more economical wash solvent and beselectively utilized in the vapor zone and for rinsing in a singlechamber unit.

The vapor zone may be effectively maintained by continuously floodingand withdrawing the generated vapor from the area above the liquid. Thismay be efficiently performed by evaporating a spray of wash solvent uponthe heat emitting section of a heat pumping system, and by directing thewithdrawn vapor over the heat absorbing section of the same system tocondense the liquid from it. This productively utilizes all of theenergy in the heat pumping system and provides a supply of pure solventfor rinsing purposes. The heat pumping type of vapor generating, solventrecovering and purifying system is of the type described and claimed inUS. Patent 3,070,463 by this same inventor.

When a mixture of solvent of differing volatility is utilized, the morevolatile component can be selectively evaporated into the vapor. Thisprovides maximum cleaning and rinsing efiiciency in the vapor zone witha relatively small amount of more volatile and expensive solvent.Rinsing with relatively cool solvent also cools the objects below thetemperature of the saturated vapor zone to condense solvent liquid uponthe objects which supplements the rinsing spray.

A vapor barrier or blanket of unsaturated air may be maintained over thesaturated vapor zone to isolate it from the ambient atmosphere and toabstract any drops of solvent clinging to the objects. This air blanketmay be maintained by continuously withdrawing air and any absorbed vaporfrom above the saturated vapor zone, cooling it to condense any solventvapor in it and returning the dry air above the vapor zone. In anapparatus open to atmosphere the dry air is returned over it at atemperature cooler than atmosphere to form a dense blanket. The rinsedobjects from the vapor zone are thus completely dried in the unsaturatedvapor air barrier or blanket before leaving the apparatus and allsolvent is retained Within the apparatus. When the temperature of thevapor zone is higher than that of the vapor barrier or blanket, the heatabsorbed from the vapor zone in the vapor barrier further unsaturates itand improves its drying efiiciency. The air withdrawn from above thevapor zone may also be advantageously cooled by the heat absorbingsection of a heat pumping system and the abstracted condensate utilizedfor rinsing. The unsaturated vapor barrier may be condensed separatelyor in conjunction with the saturated vapor zone.

The heat balance of the heat pumping system may be maintained by anauxiliary cooling section for helping condense the vapor because moreheat is emitted by a heat pump than is absorbed.

BRIEF DESCRIPTION OF THE DRAWINGS Novel features and advantages of thepresent invention will become apparent to one skilled in the art from areading of the following description in conjunction with theaccompanying drawing wherein similar reference characters refer tosimilar parts and in which the single figure is a diagrammaticcross-sectional view in elevation of a vapor degreasing apparatus thatis one embodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the figure, pump 16draws dirty wash solvent from the bottom of tank 12 of vapor degreasingcleaning apparatus 14 through filter 18. Pump 16 discharges into solventheating and evaporating chamber 20 by spraying solvent throughperforated pipe 22. Solvent evaporating chamber 20 contains the heatemitting element 24 of a heat pumping system 26 which in cludes arefrigerant compressor 28 and a heat absorbing element 30. Theseelements together with an expansion valve 32 and a refrigerant receiver34 are connected in a closed heat pumping system by piping 36. Heatemitting or rejection section 24 is, for example, the refrigerantcondensing coil of a heat pumping system 26; and heat absorbing section30 is, for example, the refrigerant evaporating coil.

Heat absorbing element 30 is enclosed within a solvent condensingchamber 38, and a vapor conduit 40 connects solvent condensing chamber38 to a cleaning machine tank 12. Solvent evaporating chamber 20, on theopposite side of cleaning machine tank 12, is connected to tank 12 byconduit 41. The outlet from conduit 41 and the inlet to conduit 40 areat about the same elevation. The elevation controls the height of thesaturated vapor zone 66 in tank 12.

Vapor produced in solvent evaporating chamber 20 is conducted by conduit41 into cleaning machine tank 12 by distribution header 45 (laterallyextended but not so shown). As saturated vapor in cleaning machine tank12 rises to the level of vapor collecting header 47 (also laterallyextended but not so shown), it spills into collecting header 47 and isconducted by conduit 40 into solvent condensing chamber 38.

Blower fan 48 induces a flow of saturated vapor into collecting header47, and, at the same time, induces flow of a vapor-air mixture 64 fromabove saturated vapor zone 66. The resultant mixture of saturated vaporand vapor-air mixture is conducted by conduit 40 into solvent condensingchamber 38. Heat absorbing element 30 converts most of the vaporentering solvent condensing chamber 38 to pure liquid solvent by coolingthe vapor to about 35 F. Blower fan 48 draws air, unsaturated with vaporinto conduit 49 and discharges a relatively cool mixture thereof intocleaning machine tank 12 through distribution header 50 (also laterallyextended but not so shown) at an elevation higher than the saturatedvapor zone. A damper 51 in conduit 49 provides a means for fineadjustment of air flow back into tank 12.

The mixture is cooler than the ambient atmosphere. Thus a relativelycool and relatively dense layer of air and vapor forms a blanket 64 overthe saturated vapor 66 in the machine. Blower fan 48 and distributionheader 50 are designed to provide a relatively slow exit velocity of airand vapor mixture. This assures its stratification and substantiallyprevents the intermixing of outside air and the resultant escape ofsolvent vapor from the top of tank 12.

Although the air returned to tank 12 through conduit 49 and distributionheader St) is saturated with solvent vapor at about 35 F., the air vaporblanket 64 itself is somewhat above 35 F. or approximately 50 F. to 60F. Therefore, blanket 64 is not saturated with vapor but is only 60 to70% saturated. Heat conducted into blanket 64 from the relatively warmvapor zone 66 below, the relatively warm air above and the sides of thecleaning machine account for some temperature increase and acorresponding reduction in saturation value or relative humidity. Sinceblanket 64 is not saturated with solvent vapor, warm parts emerging fromthe machine and passing through it dry promptly by evaporation of liquidfrom their surface.

Three factors contribute to rapid drying of parts in the air-vaporbarrier zone 64. (1) Parts passing through the saturated vapor zone '66,below, are warmed by vapor condensing on the part in final rinseoperation. (2) The air-vapor blanket is not saturated with solvent vaporand has the capacity to absorb additional vapor; and (3) The vapor rinsesolvent is relatively volatile and has a characteristically highevaporation rate.

Solvent system cycle of operation of figure Compressor 28 and pumps 16and 46 are started. Blower fan 48 is started. Pump 46 withdraws purereclaimed solvent from storage tank 62 and forces the liquid throughrinse spray nozzles 53. Cleaning machine tank 12 may either be empty ormay contain an operating charge of relatively non-volatile wash solvent.In the first case, where a homogeneous precision solvent is used alone,liquid discharged from spray nozzles 53 enters the inlet to pump 16 asthis liquid falls to the bottom of tank 12. In the second case, liquidis immediately available to pump 16.

Pump 16 supplies both the wash spray nozzles 52 and perforated pipe 22within solvent evaporating chamber 20.

As pumps 46 and 16 force liquid solvent through spray nozzles 53 and 52respectively, some of the liquid evaporates in chamber 20 and fillscleaning machine tank 12 with vapor up to the saturated vapor line 68.Thereafter, vapor enters collecting header 47 and is conducted byconduit 40 to heat absorbing element 30.

Heat taken up by heat absorbing element 30 in the process of condensingthis vapor to liquid, is promptly transferred to heat emitting element24 by the refrigerant pumped by compressor 28. As discharge pressure ofcompressor 28 increases, a pressure-operated, modulating solvent controlvalve 54 admits liquid solvent to perforated pipe 22.

The liquid solvent is distributed uniformly over heat rejecting element24 and it cascades downward in a thin film to wet the entire surface ofthe heat rejecting element 24. The more volatile precision solventcomponent such as trichlorotrifluoroethane, easily flash evaporates froma mixture containing it, and the resultant vapor enters cleaning machinetank 12 through conduit 41 and distribution header 45. Less volatilesolvent components, such as trichloroethylene, and soluble contaminants,such as oil, grease, flux, resins and the like, are returned to tank 12as liquid through drain line 55.

Solvent control valve 54 admits liquid solvent to distribution header 22and heat emitting element 24 in precisely the proper amount to maintaina constant surface temperature of heat rejecting element 24. Flow valve54 ca be adjusted to maintain any heat rejecting temperature within therange of 75 F. to F. and possibly higher. Therefore, the heat emittingtemperature can be precisely controlled to cause evaporation of aprecision solvent component while less volatile components andcontaminants are returned to cleaning machine tank 12 as liquid.Consequently, vapor in the machine tank 12 and vapor entering solventcondensing chamber 38 is substantially pure, homogeneous solvent of theprecision cleaning type. Flash evaporation without liquid boilingeliminates entrainment of contaminated liquid droplets in the vapor.

Since a heat pumping system rejects more heat than it absorbs (in theamount of heat equivalent of electrical energy supplied to thecompressor drive motor) it is inherently thermally unbalanced. Heatdissipated through conduction, convection and radiation from machinetank 12 tends to rebalance it thermally. An axially water-cooled heatabsorbing element 56 is also located in the upper part of solventcondensing chamber 38 to intercept and condense some of the solventvapor entering chamber 38. Heat absorbed by element 56 is transferred tothe cooling water and is removed from the system to ositively maintainits thermal equilibrium. Furthermore, energy supplied 3 to thecompressor motor is utilized to evaporate more solvent than otherwisewould be produced by transferral of heat from heat absorbing element 30to heat rejecting element 24.

A pressure-operated, modulating flow control valve 57 admits preciselythe proper amount of water to auxiliary heat absorbing element 56 tomaintain thermal equilibrium conditions at all times, Flow control valve57 senses discharge pressure of compressor 28 and admits cooling waterto auxiliary heat absorbing element 56 only when th temperature of heatrejecting element 24 tends to rise above the predetermined operatingtemperature and the discharge pressure of compressor 28 tends to riseabove the predetermined Operating pressure.

A third auxiliary or supplemental heat absorbing element 58 is in a heattransfer relationship with refrigerant piping 36. Supplemental heatabsorbing element 58 subcools liquid refrigerant before it is expandedwithin heat absorbing element 30. Heat absorbing element 58 may alsofunction as an auxiliary refrigerant condenser during periods whenprecision solvent is being recovered for storage in reservoir 62,particularly toward the end of the recovery cycle. Heat absorbingelement 53 may also function as an auxiliary refrigerant condenserduring periods when the cleaning machine is not in use and full recoveryof precision solvent is not desired. Water flow control valve 59 admitswater to heat absorbing element 58 only when auxiliary cooling ofrefrigerant is necessary. While cleaning operation is suspended,precision solvent remains in tank 12 and the heat pumping systemoperates periodically to maintain the cool air blanket and prevent theloss of solvent vapor. Automatic operation is easily at tained by theuse of temperatures operated and pressure operated controls ofconventional type.

The selective vapor generating aspects of this provide a simple andeconomical method of using a mixture of a relatively expensive precisioncleaning solvent, such as trichlorotrifluoroethane, and a relativelyinexpensive s lvent, such as trichloroethylene. Such selective fiashevaporation also makes it possible to utilize an azeotropic mixture forwash purpose and a substantially homogeneous precision solvent for rinsepurpose. For example, an excess of trichlorotrifiuoroethane can be addedto an azeotropic mixture of trichlorotritluoroethane and methylenechloride or to an azeotropic mixture of trichlorotrifiuoroethane andethyl alcohol. Vapor in the machine and vapor condenced to liquid issubstantially pure trichlorotrifluoroethane while wash liquid in themachine has the compos tion of the azeotrope. The parts are rapidlydried in the unsaturated air vapor zone before they leave the machinethus eliminating solvent loss by evaporation of solvent from partsoutside the machine. All of t re volatile solvent is thus purified andreclaimed for repeated use. Heat-sensitive solvents, such as methylchloroform, may also be efiiciently used in a vapor de reasing operationWithout the danger of solvent decomposition. The low temperature vaporzone also contributes to the overall efi'iciency of operation, purity ofvapor and avoidance of undue solvent losses,

Cleaning cycle of operation of figure The cleaning cycle with respect toparts or assemblies moving through the apparatus shown in the figure isas follows:

A conveyor or other means, not shown, lowers parts into cleaning machinetank 12 along the right-hand side of the tank along path 63 as shown inthe figure. Parts pass through the cool air-vapor blanket 64 then intothe saturated vapor zone 66 and between the Wash spray nozzles 52.

The parts or objects then enter the immersion wash bath at the bottom oftank 12 and are exposed to ultrasonically agitated liquid solvent toremove adherent soils.

The parts continue through the immersion wash solvent 10 to theleft-hand side of the tank shown in the figure where they emerge fromWash solvent 10 and pass through a pure liquid spray rinse from spraynozzles 53 in saturated vapor zone 66. The rinse solvent dischargedthrough nozzles 53 is relatively cool and, consequently, the parts beingcleaned are cooled to a temperature well below the temperature of thevapor in the saturated vapor zone and pure vapor promptly condenses onthem to help rinse them with precision cleaning solvent.

As the parts leave saturated vapor zone 66, they are warmed up toapproximately its temperature and Wet with liquid solvent. As theseparts pass through the relatively cooler and unsaturated air-vaporblanket zone, a combination of effects causes all liquid to evaporatefrom them. The vapor so evolved is retained in the cleaning apparatussystem as condensed rinsing solvent as the dry, clean parts pass out ofthe apparatus.

What is claimed is:

1. A method of cleaning objects by contact with a volatile solventliquid comprising the steps of washing said objects in a solvent liquidmixture incorporating components of differing volatility, selectivelyflash evaporating the more volatile of said components from a fine sprayof said solvent liquid mixture to generate vapor of said more volatilecomponent, condensing part of said vapor to provide a pure supply ofsaid more volatile solvent liquid, and rinsing said objects disposed insaid vapor with said supply of said more volatile solvent liquid.

2. A method as set forth in claim 1 wherein said selective flashevaporation is accomplished by spraying said solvent liquid mixture uponthe heat emitting section of a heat pumping system.

3. A method as set forth in claim 1 wherein said rinsing step isperformed in a saturated vapor zone above said solvent liquid mixture.

4. A method as set forth in claim 3 wherein said saturated vapor zonesubstantially consists of vapor of said more volatile liquid.

5. A method as set forth in claim 4 wherein a blanket of air-vapormixture unsaturated with said vapor of said more volat le solvent liquidis maintained above said saturated vapor zone, and said objects arepassed from said vapor zone through said blanket to dry them and toretain said more volatile solvent liquid in said blanket.

6. A method as set forth in claim 5 wherein said airvapor mixture insaid blanket is Withdrawn and cooled to condense said more volatilesolvent liquid from it to maintain said blanket unsaturated and torecover said more volatile solvent liquid from it.

References Cited UNITED STATES PATENTS 1,892,652 12/1932 Heath 20387 XR2,220,125 11/ 1940 Seaton 13411 2,265,762 12/1941 McKittrick et al. 203XR 2,755,208 7/1956 Kearney 13411 2,896,640 7/1959 Randall et al 134-11XR 2,949,119 8/1960 Smith 134-76 XR 3,030,913 4/1962 Arnold et a1 13411XR 3,070,463 12/1962 Barday 134-11 3,074,417 1/1963 Lisowski et a1 134763,106,927 10/1963 Madwed 134-76 3,106,928 10/1963 Rand 134-79 MORRIS O.WOLK, Primary Examiner JOSEPH T. ZATARGA, Assistant Examiner US. Cl.X.R. 13411, 40

